1. Field of Invention
This invention relates to a frequency domain adaptive filter and more particularly to the use of such a filter for processing and filtering sonar signals following receiption.
2. Description of Prior Art
The use of adaptive filters in analog systems which operate in the time domain has been described in a chapter by B. Widrow which appears on pages 563-587 of ASPECTS OF NETWORK AND SYSTEM THEORY, edited by R. E. Kalman and N. DeClaris, published by Holt, Rinehart & Winston, Inc., New York, N.Y., in 1970. Widrow's adaptive filter operates in an analog system and in the time domain. Widrow's filter utilizes a multi-tapped delay line with adjustable weighting from each of the taps to approximate the desired filter response. The accuracy to which the desired response can be approximated is limited by the number of taps on the delay line and the ability to weight the output from each tap. The mechanization of a filter of the Widrow type, containing a significant number of degrees of freedom so that the desired response can be clsely approximated is both mechanically and electrically cumbersome.
The system of the present invention avoids the electrical and mechanical problems associated with an analog filter of the Widrow type by utilizing a digital processing technique which operates in the frequency domain to simplify the adaptive filtering process.